This invention relates to locating systems, and more particularly to a locating system and method using a mobile communications network.
Mobile communications technology has enjoyed substantial growth over the past decade. Many cars, trucks, airplanes, boats, and other vehicles are equipped with devices that allow convenient and reliable mobile communication through a network of satellite-based or land-based transceivers. Advances in this technology have also led to widespread use of hand-held, portable mobile communications devices.
Many customers of mobile communications systems also require an accurate determination of their position, and perhaps reporting of this position to a remote location. For example, a cellular telephone in a vehicle or carried by a person offers a convenient communication link to report position information. The position information may be generated by traditional positioning systems, including a satellite-based positioning system such as the global positioning system (GPS), or a land-based positioning system, such as LORAN-C. These approaches, however, may not be suitable for particular applications that require great position accuracy.
In accordance with the present invention, the disadvantages and problems associated with previous techniques used to locate and report the position of a vehicle, person, or object equipped with a mobile communications device have been substantially reduced or eliminated. One aspect of the present invention provides a differential positioning system that integrates positioning technology with an existing mobile communications infrastructure.
According to an embodiment of the present invention, a locating system using a cellular telephone network and a positioning system includes a reference positioning receiver having known position coordinates. The reference positioning receiver receives first position signals from the positioning system and generates correction data in response to the first position signals and the known position coordinates. A transmitter site of the cellular telephone network is coupled to the reference positioning receiver and transmits the correction data generated by the reference positioning receiver. A mobile unit in communication with the cellular telephone network and the positioning system receives correction data transmitted by the transmitter site. The mobile unit also receives second position signals from the positioning system and determines the location of the mobile unit in response to the second position signals and the correction data.
According to another embodiment of the present invention, a system for locating a mobile unit within the service area of a mobile communications network includes a plurality of transmitter sites having known position coordinates, each transmitter site broadcasting time-of-arrival (TOA) data. A mobile communications device on the mobile unit receives the TOA data transmitted by at least three transmitter sites. A memory on the mobile unit stores known position coordinates of the transmitter sites. A processor receives the TOA data from the mobile communications device and determines the position of the mobile unit in response to the TOA data received from the transmitter sites and the known position coordinates of the transmitter sites stored in the memory.
Important technical advantages of the present invention include improving the accuracy of existing positioning systems using a mobile communications system. In particular, existing transmitter sites of a mobile communications network may be used as reference points to transmit position correction data to mobile units within the mobile communications network service area. Other important technical advantages include integration of communicating, locating, and reporting functions for an overall reduction in the cost and complexity of the system. For example, a differential GPS (DGPS) positioning system may use an existing communications link, such as the overhead message stream of a cellular telephone network, to send correction data from the transmitter site to the mobile unit. Important technical advantages may also include accurate and immediate position fixes without relying on calculations performed at a remote location. Other important technical advantages may also include implementation of a time-of-arrival (TOA) positioning system within the mobile communications network without land-based or satellite-based positioning technology. Other technical advantages are readily apparent to one skilled in the art from the following figures, description, and claims.